Radiation imaging systems are widely used for medical and industrial purposes. Imaging systems have been developed which use detected radiation to produce a signal which can be used to operate a visual display device or which can be used for other analyses of the pattern of detected electromagnetic radiation such as x-ray or gamma ray radiation. In such systems the radiation is typically absorbed in a scintillator material, resulting in the generation of photons of light. Light photons emanating from the scintillator are detected by the photodetectors to generate an electrical output signal that can be processed to drive the display or analysis system.
The scintillator material may be in the form of a solid block or may be divided into separate elements, such as by dicing or cutting, or by depositing the scintillator material in such a manner that individual columns or peaks are formed. It is important to protect the scintillator material from moisture absorption. For example, cesium iodide, a common scintillator material, is a hygroscopic material, that is, it exhibits a tendency to absorb moisture from the atmosphere around it; in so doing it becomes hydrolized with a consequent degradation in its luminescent properties. In a radiation detector it it is also beneficial to maximize the efficiency with which the luminescence from the scintillator is collected by the photodiodes by ensuring that the majority of photons generated in the absorption event are directed to the photodetectors.
Covering the scintillator with a thin coating is difficult due to the irregularly shaped ends or surfaces of the scintillator material, such as typically result from the common evaporative deposition processes used in formation of scintillators. Such irregular surfaces require that any coating be at least initially pliable so as to conform to the surface of the scintillator, and require that a stable and adherent surface be prepared to allow the deposition of an uniform layer of optical reflective material, such as a metal. Typical prior art imagers, such as the device of Derenzo disclosed in U.S. Pat. No. 4,672,207, do not suggest any protective or reflective coating for the surfaces of the scintillator.
It is accordingly an object of this invention to provide a protective coating for the scintillator elements of an imager, which coating will serve as a barrier to inhibit absorption of moisture by the scintillator from the atmosphere surrounding the scintillator.
It is another object of this invention to provide a protective coating that is optically reflective and substantially transparent to electromagnetic radiation of a predetermined wavelength.
It is another object of this invention to provide a radiation imaging device of improved efficiency through the use of a protective layer that is substantially impervious to moisture, is optically reflective, and that closely adheres to the uneven surfaces of a scintillator.